/Engine/Source/Runtime/Engine/Classes/Kismet/ImportanceSamplingLibrary.h
Distribute sample points proportional to Texture2D luminance.
void ImportanceSample ( const FVector2D & Rand, int Samples, float Intensity, FVector2D & SamplePosition, [FLinearColor](API\Runtime\Core\Math\FLinearColor) & SampleColor, float & SampleIntensity, float & SampleSize ) const